Answer: 15 packages of caps and 9 packages of shirts.
Step-by-step explanation: We know that caps come in packs of 3 and shirts come in packs of 5. There are 45 science club members. When you divide 45 members by the packs of 3, you get 15 packages of caps that are needed. Then you divide 45 by 5 which is 9 packages of shirts. So the science club sponsor needs to purchase a minimum of 15 packages of caps and 9 packages of shirts.